1. Field of the Invention
The present invention relates to a joined body, a high pressure discharge lamp and an assembly therefor.
2. Description of the Related Art
A high pressure discharge lamp has a ceramic discharge vessel with two end portions. Sealing members (usually referred to as a ceramic plug) are inserted, respectively, to seal the respective end portions. A through hole is formed in each sealing member. A metal member with an electrode system is inserted in the through hole. An ionizable light-emitting material is introduced and sealed in the inner space of the discharge vessel. Known high pressure discharge lamps include a high pressure sodium vapor and metal halide lamps, the latter exhibiting more superior color coordination. The lamp may be used in high temperature condition by forming the discharge vessel by a ceramic material.
In such discharge lamp, it is necessary to air-tightly seal between the end portion of the ceramic discharge vessel and a member for supporting an electrode system. The ceramic discharge vessel has a main body with a shape of a tube with two narrow ends, or a barrel, or a straight tube. The discharge vessel is made of, for example, an alumina sintered body.
A Japanese patent application No. 178,415/1999 (EP 0982278, A1) discloses the following structure. A joining portion is provided between the end portion of a ceramic discharge vessel and a member for supporting an electrode system. The joining portion has joining material contacting the discharge vessel and an intermediate layer contacting the supporting member and existing between the supporting member and the joining material. The joining material is composed of a porous bone structure with open pores and made of a sintered product of metal powder. The joining material further has ceramic phase impregnated into the open pores in the bone structure. Herewith, such joined body has improved air-tightness and resistance against corrosion, so that repeated thermal cycles does not result in the fracture of the joined body.